A method of increasing the oxygen utilization efficiency for oxygen obtained from oxygen cylinders or oxygen-concentrated gas obtained from oxygen concentrators has been proposed, wherein the oxygen is supplied only during inspiration and supply is interrupted during expiration, in order to achieve synchronization with the patient's respiratory cycle and thereby prevent waste of the oxygen supply during expiration (Japanese Unexamined Patent Publication No. 59-8972).
Devices which make use of this method include demand regulators provided with an automatic on-off valve and, respiration phase detection means mounted in the flow channel, which allow oxygen consumption to be conserved by opening the automatic on-off valve only during the patient's inspiration period and closing the automatic on-off valve during the expiration period. Such conservation is particularly effective for patients who carry the oxygen cylinder outdoors, as it allows the patient's use of the device to be extended approximately three-fold.
The respiration phase detection method used in the device may be a method of detecting temperature change by respiration such as described in Japanese Unexamined Patent Publication No. 59-8972, or a method of detecting pressure variation as described in Japanese Unexamined Patent Publication No. 2-88078. Such respiration phase detection means are used to recognize the initial point of the inspiration phase of the user, and a method has been proposed wherein the inspiration phase initial point is recognized when the respiratory signal falls on the inspiration phase side of a predetermined threshold value which is on the inspiration phase side of a standard value, or when the respiratory signal variation exceeds a predetermined variation threshold (Japanese Unexamined Patent Publication No. 2001-129086).